摘要:

In this paper, a fractal image compression system based on adaptive variable shape block transform is proposed. The procedure can be divided into approximately two basic phases: the classification phase and the adaptive shape block phase. In the classification phase, a testing image block is assigned to its own class according to its direction attribute. The direction of the block is estimated by employing the technique of projection/backprojection which is a tomographic image reconstruction skill. Due to computational complexity, only four projection directions are resolved to construct the projection classification algorithm (PCA). Computer simulations show that the proposed classification method outperforms the gradient classification algorithm. In the adaptive shape block phase, PCA and the algorithm of split/ merge are incorporated to form the variable shape block transformation. For the range blocks and domain blocks, we define fifteen merging patterns and ten shape components in the searching algorithm. Under this fractal coding approach, a better trade‐off between the decoded image quality and transmitting bit rate is performed. Several examples are presented to show the effectiveness of this coding system.

ISSN:0253-3839    

DOI:10.1080/02533839.1998.9670413

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The hydrophobic effects of PTFE‐modified Ru0.3Ti0.7O2electrodes on oxygen evolution are explored in this study by investigating contact angle, morphology and electrochemical characteristics. The hydrophobicity of electrodes is measured by the contact angle of the PTFE‐modified Ru0.3Ti0.7O2electrodes. The morphologies of electrodes with various amounts of PTFE are observed by using a scanning electron microscope (SEM) and an atomic force microscope (AFM). The effects of PTFE‐content on the electrochemical characteristics of PTFE‐modified electrodes are evaluated by the measurements of voltammetric charge, polarization and ac‐impedance. The behavior of oxygen evolution and the performance of electrodes depende significantly on the hydrophobicity of PTFE‐modified electrodes. The electrode prepared from a dipping solution with 21.1 vol% PTFE have the best performance in terms of the largest number of active sites and the highest site activity. The variation in performance of electrodes for oxygen evolution with PTFE‐content is related to the variation in active site dispersion, morphology and bubble behaviors of the electrode.

ISSN:0253-3839    

DOI:10.1080/02533839.1998.9670414

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In order to gain further understanding of aerodynamic forces and their effects on groups of high‐rise buildings, this study used wind‐tunnel experiments. Two square prisms were arranged both in tandem and side‐by‐side arrangement with different spacings in between. Similar experiments were carried out to study the interactions of aerodynamics between the two prisms when both were stationary, when only one prism oscillated, and finally, when both prisms oscillated.

ISSN:0253-3839    

DOI:10.1080/02533839.1998.9670415

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The onset of Marangoni instability of an evaporating liquid layer is studied theoretically. By assuming the surface regression of the liquid layer is negligibly small and the surrounding gas phase is asymptotically steady, similarity solutions are obtained prior to the onset of instability. Linear stability analysis is then applied to obtain the critical Marangoni number for the onset of instability. The results indicate that : (1) The onset condition is a strong function of the initial temperature of the liquid layer with which the critical Marangoni number decreases. (2) As time proceeds, the thermal boundary layer thickness near the free surface becomes larger, and the liquid layer becomes more unstable. (3) For a liquid layer with a higher initial temperature (closer to the boiling point) the most unstable mode of the disturbance shifts from a lower wave number to a higher wave number.

ISSN:0253-3839    

DOI:10.1080/02533839.1998.9670416

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

To achieve multiple performance requirements, a multi‐constrained dynamic output feedback controller is derived for linear discrete‐time systems. This paper addresses the problem of dynamic output feedback controller design subject to individual state variance constraints,H8norm constraints, regional pole location constraints and minimum auxiliary entropy constraints. By solving the inverse solutions of a Riccati‐like equation, the present approach provides the conditions and solutions for the dynamic output feedback controllers to simultaneously achieve the above four performance requirements. A numerical example is also given to demonstrate the control effect of the present method.

ISSN:0253-3839    

DOI:10.1080/02533839.1998.9670417

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This study was conducted to assess the effects of varying degrees of valvular stenosis on the flow fields in a three‐dimensional pulmonary artery model. Porcine pulmonary arteries procured from a slaughterhouse were used as test models. To produce dilated main (MPA) and left (LPA) pulmonary arteries similar to those clinically observed in valvular pulmonic stenosis, an epoxy fixation technique was employed. A three‐dimensional echocardiographic reconstruction method for color Doppler flow mapping was used to examine the flow fields in the test models. Additionally, transvalvular pressure drops were measured by a side‐hole catheter and predicted by a Doppler‐derived Bernoulli equation. Changes in flow fields in the MPA were observed as the pulmonic valve became stenotic. A jet‐like flow was present distal to the stenotic valve. The change in geometry in the MPA, due to its dilatation, had a marked effect on the pulmonary artery hemodynamics. The jet‐like flow seen distal to the valve deflected away from the centerline and impinged on the roof of the MPA. The force impinging on the stenotic valve and the roof of the MPA increased with increasing degree of valvular stenosis. Clinically, this may impair the stenotic valve and make the dilatation of the MPA more profound. The Doppler‐predicted pressure drops correlated well with the catheter‐measured pressure drops. The measured transvalvular pressure drops increased with increasing degree of valvular stenosis. As a result of increasing pressure drop, the transvalvular energy loss increased as the valve became more stenotic. Some degree of pressure recovery, reflected by a decrease in transvalvular pressure drop with increasing distance from the valve, was observed for each stenotic valve. The extent of pressure recovery increased as the valve became more stenotic. The study demonstrates the necessity of considering complex biological flows from a three‐dimensional viewpoint.

ISSN:0253-3839    

DOI:10.1080/02533839.1998.9670418

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Complexity C can characterize the order or disorder of a time series and was used to discriminate between normal and abnormal electroencephalograms (EEG) in this study. Two classified groups of 20 normal and 20 apoplectic subjects were chosen for this experiment. Two segments of sixteen‐channel EEG signals for every subject were measured by unipolar recording and Laplacian montage. The results for both groups showed that the EEG signals were neither pure compound (quasi) periodic waves nor white noise, and the statistical C values were almost independent of the chosen EEG segment, no matter what montage was adopted. Moreover, the statistical C values showed little significant difference between EEG data collected by unipolar recording and Laplacian montage for both populations. In addition, no matter what montage was taken, the values of C for the normal population weresignificantly higher than those of the apoplectic population at the 0.01 confidence level for each corresponding channel. In discriminating between normal and abnormal subjects by complexity C, two pattern recognition methods were applied and a recognition rate of 95% or above was obtained. We conclude that the measuring complexity C is a much simpler and more efficient method for clinical EEG diagnosis.

ISSN:0253-3839    

DOI:10.1080/02533839.1998.9670419

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The Delaunay triangulation is broadly used on flat surfaces to generate well‐shaped elements. But the properties of Delaunay triangulation do not exist on curved surfaces whose Jacobians are different. In this paper we will present a modified algorithm to improve the shape of triangulation for the curved surface. The experiment results show that making use of “mapping factors” in the Delaunay triangulation and Laplacian method can produce better mesh (most aspect ratios≤3) on a curved surface.

ISSN:0253-3839    

DOI:10.1080/02533839.1998.9670420

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The active comb filter without the use of inductors is very useful for removing harmonic noise such as power line interference in bio‐medical signals. This paper presents an approach for the design of an active comb filter. A table composed of 62 bandpass filters is proposed, which can be used in the design of the presented active comb filter. Simulation results and performance tests are given to demonstrate the feasibility of the presented active comb filter

ISSN:0253-3839    

DOI:10.1080/02533839.1998.9670421

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The strength of lightweight aggregate concrete depends basically on the mortar strength and the packing strength of lightweight coarse aggregate. The former can be adequately estimated based on the water/cement ratio, but there has been no appropriate method to determine the latter. In this study, a series of experiments were carried out to explore a method to evaluate the packing strength of lightweight coarse aggregate. Test results have shown that for lightweight aggregate concrete a dividing strength indeed exists. In addition, the dividing strength can then be reasonably adopted as an indicator in representing the packing strength of lightweight aggregate. Finally, as the maximum size or the volume content of the coarse aggregate varies, the corresponding packing structure and the packing density of the lightweight concrete will be different, leading to a change of the dividing strength.

ISSN:0253-3839    

DOI:10.1080/02533839.1998.9670422

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor